Translucent paper



United States PatentO TRANSLUCENT PAPER William H. Griggs and Martin Salo, Rochester, N. Y., as-

signors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application February 9, 1953, Serial No. 336,015

2 Claims. (Cl. 96-85) This invention concerns treatment of paper to render it translucent.

Paper is treated to render it translucent for many products, such as tracing paper used in drawing, parchment used in lampshades, master prints in making blueprints and the like. Accordingly, a great variety of processes have been devised to translucentize paper depending upon its intended use.

For instance, paper has been treated with sulfuric acid which swells the fibers of cellulose to the point of producing a gelatinous mass. The process is then arrested by washing with water and, the gelatinous cellulose which is precipitated in the still remaining fibers of the body, acts as a cementing material resulting in a sheet having translucence, waterproofness and creaseproofness.

In addition, U. S. Patent 1,996,858 discloses a method for making translucent paper by impregnating the paper with ethyl or methyl abietate and sucrose octoacetate in a volatile solvent such as ethylene dichloride. Some methods use oily substances such as mineral oils, rosin oils or the like.

In the copying of engineering and architectural drawings, it is customary by photographic means to make a master copy from which are made successive copies of the drawings for use by various contractors and sub-contractors. The speed in making these copies is determined by the amount of light transmitted through the translucent paper backing on the photographic master copy. Therefore, suitable paper for this purpose must have a high degree of transmission of light and must form a suitable support for a photographic emulsion. Translucent paper made according to previously known methods and tracing paper now on the market are often found to have characteristics which render them unsuitable in some respects for photographic use. For instance, many translucent papers have an oil treatment which renders the paper surface greasy so that oil or grease is transmitted to paper which has been brought into contact with the treated surface. Methyl abietate while suitable in many respects for rendering paper translucent may become unstable with aging and become yellow. Other papers are found to present surfaces which do not readily accept a photographic emulsion and which require subbingto permit adhesion of the emulsion. Papers which have been treated with some resin compounds give up these resin compounds when immersed in photographic solutions used in processing photographic paper. Others will not stand erasing but abrade so that the erased area cannot be written upon with ink.

We have discovered a process for producing a photographic tracing paper which is superior to previously known translucent paper in regard to controlled light transmission, chemical stability, stain resistance and erasing characteristics. In addition, our method can be used on cloth. It can be used, if desirable, without volatile solvents, rendering our process less expensive to use and less hazardous.

The primary object of this invention is to provide a Patented Sept. 3, 1957 photographic translucent paper. Another object of this invention is a translucent paper which can be erased without damaging the paper surface.' A further object of this invention is to provide a method for rendering a paper transulcent which may be used if desired without a volatile solvent and elaborate solvent recovery equipment. Another object is a transulcent paper with good aging qualities, compatible with photographic emulsions, practically odorless, and having controlled translucency. Another object is to provide a method of treating cloth, paper or similar material to render it translucent for photographic purposes.

We have found that certain mixtures, resins and plasticizers can be combined and applied either with or without solvents and yet give a base stock of good light transmission. We have discovered that polymerized alpha-methyl styrene either used alone or with a suitable plasticizer, such as dioctyl phthalate, or dibutyl sebacate can be used in our process. The polymerized alphamethyl styrene is normally a viscous substance with a viscosity of from -1000 op. at 60 C. Consequently,

it is desirable to use heat to facilitate applying the alphainvention comprises coating a mixture of polymerized alpha-methyl styrene and dibutyl sebaccate using a hot melt coating machine in which the coating solution is kept at a temperature of about 200 F., and then passing the paper between heated calendering rolls. However, higher temperatures may be used depending upon the nature of the stock since our invention may be used with any suitable adsorbent base. The lower limit for the temperature depends upon the viscosity of the coating composition which, in turn, will vary depending upon solvents, if any, which may be added, and the ratio of polymer to plasticizer.

Various methods may be used of applying the resins and plasticizers to the base material. For instance, the paper or cloth may be immersed in the coating material and squeezed between rolls, or it may be applied using a scraper bar or a calender nip. The amount of the polymer which is impregnated in the interstices of the paper also depends upon the time that the paper is immersed or remains in contact with the coating solution. Consequently, varying the rate of speed of the paper through the coating machine will produce variations in the fin al product. 7

In order that the process may be more fully understood, the following specific examples are given by way of illustration of the preferred embodiments.

EXAMPLE 1 A 10" roll of paper (100% rag stock, 12 lbs. per 1000 sq. ft.) was passed between 2 heated steel rolls under pressure. A mixture of polymerized alpha-methyl styrene and dioctyl phthalate in a 2 to 1 proportion was applied at the nip on one side of the paper and the excess was EXAMPLE 2 A 10 roll of paper stock (100% rag stock, 12 lbs. per 1000 sq. ft.) was passed between two heated rolls under pressure. A mixture of alpha-methyl styrene polymer and t 3 dioctyl phthalate in a 2 to 1 proportion was applied at the nip on both sides of the paper and the excess was squeezed 01f during passage between the rolls. The steel rolls and impregnating .compositionwere kept at a temperature of 200-225 F. The resulting opacity was 39 to 42%.

EXAMPLE 3 Examples of the translucent stock from Examples 1 and 2 were sensitized with light-sensitive photographic emulsion and a suitable print was made on the sensitized paper. After drying, the lines of the print were easily erased with either a dry or a wet typewriter eraser without the stock being abraded.

EXAMPLE 4 Solvent coating Resin: Paper Stock Plasti- Solvent Percent cizer Opacity Ratio Ethylene chloride 2:1 Ethylene chlon'detoluene 52 mixture (1:1, 4:1, 1:4). 4:1 Toluene, Be)nzene (same sol- 52 vent range 100% Rag Ethylene chloride 2:1 Resin 65 50% Resin. 1 2:1 Ethylene chloride 52 Ethylene chloride: 100% Pulp, 12# 2:1 20% Resin 65 Resin 40 l Dibutyl sebacatc used instead of dioctyl phthalate.

Hot melt coating Resin: Percent Paper Stock Plasticizer Opacity Ratio 1:0 2:1 4:1 52 6:1 Reg, 12# Stock Sized 4:1 40

48 2:1 4:} "a; 100 Ra 205i 2:

A, g 2:1 28 100% Pulp, 12# 4:1 43 100% Pulp, 223 2 1 48 100% Rag, non-tub sized 21% 2:

It has been found desirable to increase the light transmission of photographic base stock to improve the print back speed of master copies when used on such machines as the Revolute and Ozalid machines. As shown above, our process can be used either with or without the use of organic solvents. When used without a volatile solvent this process makes it possible to produce a high grade of translucent paper using paper mill equipment.

We claim:

1. In the process of preparing a translucent paper for photographic purposes, the steps which comprise coating one side of the paper with a coating comprising amixture of polymerized u-methyl styrene and a plasticizer selected from the group consisting of dioctyl phthalate, dibutyl phthlate and dibutyl sebacate at a temperature within the range of 200-225 F., passing the coated paper between heated rollers at a temperature within the range of 200225 F. and coating the paper with a photographic emulsion containing light-sensitive silver halide salts.

2. A photographic translucent paper produced by impregnating the paper with a mixture of polymerized r-methyl styrene and a plasticizer selected from the group consisting of dioctyl phthalate, dibutyl phthalate and dibutyl sebacate at a temperature of from 200225 F., passing the paper between heated steel rollers at a temperature of 200-225 F., and coating with a photographic emulsion containing light-sensitive silver halide salts.

References Cited in the file of this patent UNITED STATES PATENTS Wood Ian. 9, 1951 Salo et al Apr. 21, 1953 John Wiley, 1952, pages and 136. (Copy in Div. 50.) 

1. IN THE PROCESS OF PREPARING A TRANSLUENT PAPER FOR PHOTOGRAPHIC PURPOSES, THE STEPS WHICH COMPRISE COATING ONE SIDE OF THE PAPER WITH A COATING COMPRISING A MIXTURE OF POLYMERIZED A-METHYL STYRENE AND A PLASTICIZER SELECTED FROM THE GROUP CONSISTING OF DIOCTYL PHTHALATE, DIBUTYL PHTHLATE AND DIBUTYL SEBACATE AT A TEMPERATURE WITHIN THE RANGE OF 200-225*F., PASSING THE COATED PAPER BETWEEN HEATED ROLLERS AT A TEMPERATURE WITHIN THE RANGE OF 200-225*F. AND COATING THE PAPER WITH A PHOTOGRAPHIC EMULSION CONTAINING LIGHT-SENSITIVE SILVER SALTS. 